Radio Broadcast (May 1928-Apr 1929)

DECEMBER, 1928 PROBLEMS IN SYNCHRONIZING TELEVISION DISCS 125 Table II. New U. S. Television Licenses Call 4XA 2XBV 6xc 2XBS 8x1 IX AY 2XBU 3XK 8x1 2XBW Location White Haven, Tenn. New York City Los Angeles, Calif. New York City East Pittsburgh, Pa. Lexington, Mass. Beacon, N. Y. Washington, D. C. East Pittsburgh, Pa. Bound Brook, N. J. Power in watts 5,000 5,000 ) 15,000) 5,000 20,000 500 1 100 ) 5,000 20.000 ) 5,000} Wave Band* in meters 125-120 66.67-65.22 65.22-63.83 63.83-62.5 62.5-61.22 61.22-60.00 19. 86-19. 73 1 Each band 100 kc. wide The motor disc and neon lamp were put in a darkened box. A double-pole double-throw switch changed the lamp from amplifier to local a.c. to check motor synchronism, but it was always found in step. A stop watch timed the number of seconds taken by the image of a spoked wheel to make one complete revolution. There being four poles to the 1800 r.p. m. motor this meant a gain or loss of two cycles per revolution of the wheel image. If the "wheel" moved in a direction opposite to that of the disc the received frequency was leading the local frequency. While it is not certain the local frequency was exactly 60.0000 cycles during this test it generally is found to be very close to this, and synchronous clocks in the vicinity (Jamaica, Queens County, N. Y.) keep very good time. This is more or less confirmed by the fact that about as many of the frequencies measured were found higher as were lower. The observations listed in Table I were taken July 24, 1928, the time being Eastern Daylight-Saving time. The hours during which the tests were made represent possibly extreme power load fluctuations between sunset and evening darkness when lights were being switched on, but also this is the time when most people would be using their television receivers. Due to the quite uniform motion of the "wheel" it could be followed on code stations and none of the amateurs listed know that they participated in this test, it being unnecessary to get in communication with them on the local transmitter. Where the seconds required for a revolution of the "spoked wheel" are a few it means it was revolving fast and indicated a great deviation from the local standard frequency. A great number of seconds for one turn in either direction indicates close to but not quite synchronism. The stations with calls beginning with the numeral "2" that are shown probably were operated from the same power network. Three distant stations had to be listed as being in exact synchronism because for the duration of the measurement, usually two minutes, no variation in their frequency could be noted. Such are probably rare coincidences and if measured for a quarter hour would probably show slow creeping of frequency. Two others came quite near this standard. Due to peculiarities of transmitter circuits, or filters producing frequencies that were multiples of 60 cycles, additional "spokes" were present for some stations, oftentimes eight, occasionally twelve or sixteen, but it was not very hard to time one revolution if the modulation was strong. The method of collecting the data as explained above is so similar to what would happen in attempting television by synchronous motors on these power supplies that the answer can be read directly from the notes or data. A synchronous television motor running 900 r.p.m. would, however, take twice as long to get out of step as the figures under the column headed "Sec. per APPARATUS USED BY MR. PHELPS IN CHECKING POWER-LINE FREQUENCIES NEW TELEVISION PROJECTOR This apppratus was exhihiied at the German Radio Exposition in Berlin by Prof. Karolus of Leipzig Rev." A better statement of the case would be to say that (except for local stations) there would be no picture practically all of the time, but that every so many seconds the picture would appear correct for a moment. This puts a different angle on the problem and a vote taken amongst television friends seems to indicate that if nonsynchronism must be tolerated they would prefer having the picture come flitting in right every second or so rather than spreading out with long periods between correct p\ctures. In other words, almost exact synchronism would be more of a nuisance than a moderate variation, which is an unlooked for conclusion! The data, even allowing a ten per cent, error in some of the readings, forces us to admit that synchronous motor operation from lines out of our own network is far from satisfactory and thus one more hope for simple synchronizing is shot to pieces. We now understand the hesitancy of the big radio companies in not placing complete televisors on the market immediately after the first public demonstrations. Television to-day is in about the same stage as the old chain-drive, stem-wind horseless carriages of not so long ago, but how many goggled drivers of those days now regret their early escapades when a driver had to be a mechanic? By the time this article is published television probably will have made several notable advances. A more interesting and fruitful field for individual experiment is difficult to find. Book Review "A Laboratory Treatise on B Battery Eliminator Design and Construction." Published by Radio Treatise Company, New York City, 87 pages. Price — $1.00. HpHE text of this book is intended to set forth * the essential principles of the design and operation of B-power units. The book is divided into several major sections as follows: Power Transformers, Rectifiers, Condensers, Filter Chokes, Calculation of Resistances, C-Bias Voltages and Resistances, and General Considerations. The last page of the book contains an index. In the various chapters the functioning of the component parts of a B-power unit is considered. Probably the major problem one confronts in the building of a B-power unit is the choice of the apparatus; that is, deciding what rating it should have and what capacity. The author discusses these subjects quite fully, and indicates the sort of power transformers which should be used with different B units, the value of the chokes, filter condensers and resistors. The dictionary being the only book in which one probably can't find an error, the typographical errors (of which there are quite a few) in this book may be excused. Technically the book seems to be sound, although some serious errors are to be found. For instance, on page 57 the author states that, in connection with a.c. voltages, "the average voltage is that value indicated on our a.c. voltmeter." Actually an a.c. voltmeter reads effective values. Average voltages are also confused with effective values in the statement that, "the peak voltage is equal to 1.4 times the average value." The chapter on filter condensers, page 60, states that if two condensers with similar ratings are connected in series, the total voltage across them may safely be twice the rated voltage. A diagram is given showing two condensers so connected. This is one instance where we cannot recommend that the author's suggestion be put into practice. When two condensers are connected in series across a source of d.c. potential, the division of voltage between the two condensers depends not at all on their respective capacity — it depends entirely on their resistance. However, in spite of these points about which we differ with the author, we want to assure the reader that the book contains a potpourri of exceedingly helpful data. Its low cost puts it within the reach of all of us and it is certainly a worth-while addition to a library of elementary radio texts. — H. E. R.